I managed to power the USB host shield by the connector 7-12v (green screw connector) as well as the Arduino nano. Both boards are powered (Power LEDs are on).

However, my USB stick (communicating with a joystick by RF) is not powered on when I plug it in the USB connector of my USB host shield.

My initial guess was that the host shield was configured in peripheral instead of host. I read in the spec of MAX3421E (HERE) that I might need to switch to HOST mode.

Does anyone have a single clue how to do it? I'm really new to the world of board programming. Apparently I have to rewrite one of the register with the value "1" (the HOST mode bit) but I don't have any idea how to do it.

According to the schematic of the USB host adapter the USB port should be powered if the board is powered but the power is fused (I guess with a 500mA fuse but that isn't specified). So if your stick does not get power it uses to much current for this shield.

Test using a much simpler USB device such as a keyboard. Keyboards usually draw less than 100 mA. A radio gadget might draw hundreds of mA. Run the board_qc sketch and post the serial console output.

Check the voltage of the power supply connected to the 7-12V connector on the host board. Is it 7V or higher? What is the maximum amount of current the power supply can provide? Check the 5V and 3.3V rails on the USB host board. Check for 5V on the USB connector.